CA1074688A - Mixed-firing burners for use with pulverized coal and heavy oil - Google Patents

Abstract

Specification Title of the Invention Mixed-firing Burners for Use with Pulverized Coal and Heavy Oil Abstract of the Disclosure A heavy oil supply pipe, a protective pipe, an air supply pipe for burning heavy oil, a coal-air supply pipe, a coolant supply pipe and a protective caster are arranged concentrically in the order mentioned. A coal whirler and an air whirler are provided to inpart whirling motions to coal flame and heavy oil flame for thoroghly admixing them.

Description

~746~3 Back round of the Invention g This invention relates to a mixed-firinq burner for use with pulverized coal Chereinafter simply referred to as coal) and hea~y oil and utilized in a combustion furnace for use in cement kilns or boilers.
For the purpose of effectively using coal which is more a~undantly available than petroleum, there have been used burners which emplo~ exclusive firing with coai ~com-bustion by coal itselfl or mixed-firing with coal and heavy oil.
In the former t~pe burner, since the length of the flame is long, high combustion temperature can not be obtained with the result that it is difficult to obtain perfect combu~tion and the efficiency of heat utilization is low~ In burners which employ exclusive firing with heavy oil Ccom~ustion by heavy oil itself), on the other hand, since the oil burns well and the length of the flame is short~ it is possible to reali~e high combustion temper-atures. For this reason, the defects of the burner for ' . '.
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-` ~L07~6~38 excl~sive use wi~h coal can be eliminated by firing or burning a mixture of coal and heavy oil.
According to the conventional method for the mixed firing, pulverized coal and heavy oil are blown into the burner through parallelly disposed discrete burners or a mixture in which pulverized coals are suspended in heavy oil is burned. However, where pulverized coal and heàvy oil are blown into the furnace through separate burners, due to the difference in the comhustion character-istics of the Plames of coal and heavy oil, it is difficult - to obtain satisfactory combustion state, and where pulverized coal is suspended in heavy oil, it is necessary to incorporate an additive for the purpose of improving dispersion of the pulverized coal and preventing prepicita-tion of the ; 15 same, thus complicating the operation and increasing the cost of fuel.
Summary of the Invention - Accordingly, it is an object of this invention to provide a burner having compact and rugged construction and 20- being capable of efficiently effecting mixed-firing with heavy . oil and pulverized coal.
~ ~nother object of this invention is to provide a . novel burner capable of changing the ratio of heavy oil and - pulve~ized coal to any desirable ratio thereby producing any desired heat quantity.
Still another object of this invention is to provide a burner fox mixed-firing wîth pulverized coal and heavy .~ oil in ~hich deposition and dry distillation of the pulverized coal on the wall of the coal-air mixture supply pipe can , ' ' . ' .
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be preven~ed.
In accordance with this invention these and fnrther objects can be accomplished by providing a mixed-firing burner for use with coal and heavy oil comprising a heavy oil supply pipe having a burner tip at one end; a protectiYe pipe surround-ing the heavy oil supply pipe; a pipe for supplving air necessary to burn heavy oil and surrounding the protective pipe, the air supply pipe being provided with a guide pipe in its front end;
a coal air supply pipe concentrically surrounding the air supply pipe for supplying a mixture of pulverized coal and air; a perforated plate provided at the fore end of the air supply pipe for lnterconnecting the guide pipe and the air supply pipe, the perforated plate having a great number of perforations formed therein; a cooling medium supply pipe and a protective caster successively surrounding the coal-air supply pipe 7 the cooling medium supply pipe being supplied with air and having a front end opened to the outside; an air whirler provided between the tip of the protective pipe and the guide pipe; a coal whirler provided between the tip of the air supply pipe and the coal-air supply pipe; and an intermedlate whirler located at an intermediate point along the length of the coal-air supply pipe.
Brief Description of th_ Drawings Further objects and advantages of the invention can be more fully understood from the following detailed descrip-tion taken in conjunction with the accompanying drawings in which:
Fig. 1 is a sectional view showing the portions of the furnace near burners;
Fig. 2 is an enlarged cross-sectional ~riew of the furnace shown in Fig. 1 taken along a line II-II;

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Fig. 3 is an enlarged cross-sectional view of one burner taken along a line III-III of Fig. 4;
Fig. 4 is a longitudinal sectional view of the burner shown in Pig. 3;

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Fig. 5 is an enlarged longitudinal sectional view of a burner tip incorporated in the burner according to the inventicn;
Fig. 6 is an enlarged cross-sectional view of Fig. 5 5 taken along a line VI~
Fig. 7 is a cross-sectional view o~ Fig. 4 taken along a line VII~VI~:
Fig. 8A is a top view of an air whirler;
Fig. 8B is a cross-sectional ~iew of Fig. 8A taken 10 along a line VIIIB-VIIIB;
Fig. 9A is a schematic diagram of one example of a source of the mixture of air and pulverized coal; and Fig. 9B is a cross-sectional view of a portion of the source shown in Fig. 9A.
15 Description of the Preferred Em~odiment - Figures 1 and 2 show an application of this invention to a rotary kiln 1 for firing cement. The rotary kiln 1 is supported ~ rollers 2 and its one end is enclosed in a hood 3. ;
clinker cooler 4 overlain ~y a grate is housed in the lower 20 portion of the hood 3 and a cooling fan 6 is connected to the bottom of the hood so as to pass cooling air injected as shown an arrow A through the grate 5 and a layer 7 of fired cement on the grate. A portion of the heated air enters into the ~ -rotar~ kiln 1 and is drawn out of a port 100 to act as the secondar~ air while the remaining air is conveyed to a Cottrell precifitator~ not shown. The secondary air from the port 100 is used to dry pulverized coals.
A plurality of grates comprised of the grate 5 are arranged to overlap with each other with a slight inclination ' , . ' ~ .
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as ~hown in Fig. 1. The ~ates, every other, reciprocate bac}c and forth 50 ~hat clinkers are conve~ed from left to right and - during this conveyance, clinkers o~ a small slze slip off through the grate onto a conveyor and clinkers of a large size carried on the grate 5 are directly exposed to the cooling air, thereby being cooled efficientl~v. The large sized and small sized clinkers are finally delivPred in the direction shown by an arrow B.
A burner 8 is mounted on the hood with its discharge end directed toward the kiln. As shown in Fig. 2, two burners -8 are provided which are offset from the axis of the kiln by -taking into consideration their positions relative to the fired cement. However, the number of the burners is not limited to two.
As shown in Figs. 3 and 4, each burner 8 comprises heavy oil supply pipes 10 ~in Fig. 4, illustrated by a solid line for simplification) each having a burner tip 9 and surrounded b~ a protective pipe 11. An air suppl~ pipe having guide pipes 12 on its inner or fore end and suppl~ing air for burning heavy oil in provided to surround the protective pipes 11, and the guide pipes 12 and the air supply pipe 13 are interconnected by a perforated plate 14 provided at the fore end of pipe 13.
The intermediate portions of the protective pipes 11 are supported by a supporting plate 26. The heavy oil is atomized by constructing the tips 9 so as to impart a whirling motion to the heavy oil. The burner tip 9 will be detailed later with reference to Figs. S and 6. The perforated plate 14 is provided with a number oE perforations having a diameter . .

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~74~813 of several milimeters for example, 3mm or 6mm, for passing air through an air whirler having guide blades and the perforated plate 14. The air passing through the perforated plate 1~ cools it and prevents it from burning. Furtheremore, the air stirs coal flame and heavy oil flame to enhance their mixing. In this embodiment, the burner tip 9, heavy oil supply pipe 10, protective pipe 11, and guide pipe 12 are provided in duplicate. Between the -tip of each protective pipe 11 and the tip of each guide pipe 12 is provided an air whirler 15 secured to the protective pipe 11 alone. The whirler 15 comprises, as shown in Figs.
8~ and 8Br a plurality of radial blades 16 which are spaced apart in the circumferential direction and skewed about the axis.- ~ccordingly, the air for burning heavy oil is imparted with a whirling motion when it passes through the whirler 15. The whirling air is well admixed with the heavy oil ejected from the heavy oil burner tip 9 to assist atomization of the heavy oil. Accordingly, the heavy oil flame and the coal flame are efficiently admixed thus improving the com~ustion. The inlets lOa of the heavy oil supply pipes 10 are connected to a source of heavy oil, not shown, and the inlet 13a of the air supply pipe 13 is connected to a source of air, not shown. Concentrically with the air supply pipe 13 are provided a coal-air supply pipe 17 which supplies a mixture of pulverized coal and air, a pipe 18 for passing cooling medium, and a caster 19 made of an amorphous fire-proof material for protecting the burner, in the order mentioned. A coal whirler 20 having the sa~e construction as the air whirler 15 shown .

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in Figs. 8A and 8B is provided be-tween the tips o~ the air supply pipe 13 and the coal-air supply pipe 17. The whirler 20 imparts a whirling motion to the mixture of air and pulverized coal passing therethrough. The inlet 17a of the coal~air supply pipe 17 is connected to such . a source of the mixture of air and pulverized coal as shown in Figs. 9A and 9B.
This source is shown as an arrangement comprising a pressurized air source, a regulator valve ana a coal feeder.
The regulator valve delivers a desired amount o air into a nozzle pipe in an arrow direction. The coal ~eeder has a casing 90 which is partitioned into two, upper and lower, chambers. Rotatably mounted concentrically with th~ casing ~ 90 is a shaft ~hich is driven by a motor 92. The shaft is rigidl~ mounted with an upper group o~ blades 93 and a lower group o~ blades 93, these groups being separated b~ a partition wall. ~ig. 9B shows the group of six blades.
~hen the motor 92 is energized, pulverized coals are fed through an inlet 91 into the upper chamber.. As the blades rotate, a desired amount of the pulverized coals confined in a space between adjacent blades are transported toward an opening 94 formed in the partition wall and then, aropped into the lower chamber in which these pulverized coals ~ .
~re conye~ed to an outlet so as to be drawn out in the direc-tion shown b~ an arrow C. Thus, the pul.verized coals are admixed with the pressurized air so that a mixture o~ pulverized coals and air having a desired mi~ing ratio is delivered in the direction shown by an arrow D.
~n intermediate ~,~hirler 22 is prov~.d.ed hetween . .
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the air supply pipe 13 and the coal-air supply pipe 17 and secured to the air supply pi.pe 13. Whirler 22 has a construction similar to those of whirlers 15 and 20 and imparts a ~rhirling motion to improve admixing of air and 5 . pulverized coal. The whirler 22 cooperates with~the coal whirler 20 to make uniEorm the concentration of the pulverized coal ejected through burner 8 thereby improving combustion of admixed coal and heavy oil. The inter~ediate whirler 22 also prevents the pulverized coal -Erom depositing on the intermediate portion and -then converted into coke by dxy distillation. A wear proof arcuate protective cover 24 is provided about the periphery of the air suppl~ pipe 13 at portions facing the inlet of the coal-air supply pipe for preventing the air supply pipe 13 from being damaged b~ the collision of the pulverized coal. Preferably, as . .
shown in Fig. 7, the protective cover 24, made of a steel ~
material, is so constructed as to have a ridge which acts ~
as if it were a watershed. ~.,`.
As the cooling medium may be used water or air. :~
Howevert when water is used so that the pipe 18 is construc-tionally closed at its front end, it leaks through cracks which might be ~ormed in the wall of the pipe 18 so that it is advantageous to use air in which case the tip of :~
the pipe 18 is arran.ged in concentric with the coal-air ~.
supply pipe 17. Cooling air is supplied from a source of c:ooling air, not shown, into the pipe 18 through an .inlet poxt 18a. By cooling -the coal-air supply pipe 17 from outside by the cooling medium flowing through pipe 18, the -temperature inside oE the pipe 17 can be maintained 7~6~

at about 150~C, ~or example, thereb~ not only preventing deposition oE the pulverized coal onto the inner wall of the pipe 17 but also preventing ignition o~ the pulverized coal in the burner 8 -thus preventing back fire. This also S prevents disintegration o~ the caster due to overheat. When cooling air is used, it is possible -to prevent excessive spreading o~ the mixture of the coal fIame and the heavy oil ~lame, thus assuring efficient combus-tion.
The protective caster 19 surrounding the cooling medium supply pipe 18 is supported b~ a plurality of studs secured to the periphery o~ pipe 18, and a protective ring 27 made o~ heat resistant cast steel is mounted on the tip of the caster which surrounds the tip o~ the burner.
The heavy oil supply pipes 10, the protec-tive .~ ~5 pipes 11 and the air whirler 15 are mounted to be integral and slidable in the axial direction. By tightening or releasing a ~olt 400, the protective pipe 11 together with pipe 10 and whirler 15 is axially moved relative to the air supply pipe 13. The air supply pipe 13, the coal whirler 20 and the guide pipe 12 are also moun-ted to be integral and slidable in the axial direction. ~y tightening or releasing a bolt 401, the air supply pipe 13 together with guide pipe 12 and whirler 20 is axially moved relative to the coal-air supply pipe 17. Numerals ~OOa and ~Ola designate bellows. For these axial movements, more steady but complicated arrangernent such as ~or example a rack and pinion mechanism or a piston-cylinder mechanism may be emplo~ed. ~t -the commencemen-t o~ firing, such axial adjustments are carried out to obtain a desired flame ~, _ condition. In this manner, the combustion condltion can be varied as desired by changing the positions of heavy oil ejection and alr ejection or by changing the whirling positions of air and o-F the mixture oi pulverized coaI and air.
In addition , it should be appreciated that the ~osition of burner tip 9 relative to the protective pipe ll is also responsible i'or the combustion condition. When the burner tip 9 is flushed with the protective pipe ll, the flame spreads. When the burner tip 9 is recessed relative to the protective pipe ll, the flame becomes thin, Fiys. 5 and 6 show one example of a burner tip 9l in the form of a pressurized oil spray type, which is incorporated into the burner of this invention. The burner tip 9 comprises a cylindrical sleeve 51, a front plate 52~ a rear plate 50 screwed to -the cylindrical sleeve 51, and an internal member 53 having a conical tip which opposes an openiny 57 formed in the front plate 52 and formed with an ~nnular recess 54 and a plurality of borings 55. The heav~ oil supply pipe 10 is coupled with the rear plate 50~ Thus, heavy oil from the heavy oil supply pipe inlet lOa connected to a pressurized oil source not shown, is passed in the direction shown by an arrow E into the burner tip 9r directed to the annular recess 54 through a plurality of transverse conduits 60 ~See Fig. 6), passed throuyh the lonyitudinal borings 55 to reach a space 56, and finally ejected through the openiny 57.
Where only one burner 8 is used, the direction - of whirliny of air mixed with heavy oil and oi the mixture of pulverlzed coal and air, that is the direction of twisting ~` 1~74~88 the flame may be clockwise or coun-terclockwise, bu-t when two or more burners are used as shown in Fig 2, it is advantayeous to make different the directions of the air whirler 15 and of the coal whirler 20, for example one in the clockwise direction and the other in the counter-clock~ise direction, for improving the combustion condition ;n the ki]n.
The pulverized coal may have a size of 200 mesh specified b~ JIS CJapanese Industrial Standard) or 4900 mesh specified by DIN ~Deutch Industrie-Norm) and it is advantageous to use a velocity of 120m/sec of air ejecting from the air supply pipe 13, and a velocity of 55m/sec of the coalair mixture ejected from the coal-air supply pipe 17~ a velocity of 27m/sec of the cooling air ejected from the cooling medium supply pipe 18, and a velocity of 50m~sec of the air ejected from the perforated plate 14~ ~
As above described, according to this invention ~ ;
since heavy oil, air and pulverized coal are ejected concentri-call~ through the same ~urner for effecting mixed-firing ~ith the heav~ oil and coal, the coal flame and the heavy oil flame are thoroughly admixed thereby improving the efficienc~ o~ combustion. Accordingly, it is possible not onl~ to make compact the burner but also to eliminate difficulties encountered where coal and heavy oil are - burned separately. By the mixed-firing of coal and heavy oil~ it is possi~le to increase the combustion temperature ~han the ~urner for exclusive use with coal, thus increasing the efficienc~ of heat utillzation.

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When an in-termediate whirler is provided for the coalair supply pipe, it is possihle -to prevent deposition of the pulverized coal and dry distillation oE such deposited coal.
According to this invention by varying the ratio of admixed pulverized coal to heavy oil from 25 to 75%
by weight by means of the arrangement such as shown in Figs, 9A and 9B, it is possible to vary the rate of combustion and heat quantit~ to any desired values.
~oreover, by effecting mixed firing of C heavy oil containing a relatively large amount of sulfur, e.g~

2 to 3% and pulverized coal containing a relatively small ~uantit~ of sulfur, e.g. about 0~3%, it is possible to provide an advantageous effect of using a fuel of low sulfur content, thus decreasing environmental pollu-tion.
It is also possible to use pulverized coke or ~-other combustible substance instead of pulverized coal. ~ ;
Where pulverized plastics are used, the problem of discarded plastics can be readily solved.

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A mixed-firing burner for use with coal and heavy oil comprising a heavy oil supply pipe having a burner tip at one end; a protective pipe surrounding said heavy oil supply pipe; a pipe for supplying air necessary to burn heavy oil and surrounding said protective pipe, said air supply pipe being provided with a guide pipe in its front end; a coal air supply pipe concentrically surrounding said air supply pipe for supplying a mixture of pulverized coal and air; a perforated plate provided at the fore end of said air supply for interconnecting said guide pipe and said air supply pipe, said perforated plate having a great number of perforations formed therein; a cooling medium supply pipe and a protective caster successively surround-ing said coal-air supply pipe, said cooling medium supply pipe being supplied with air and having a front end opened to the outside; an air whirler provided between the tip of said protective pipe and said guide pipe; a coal whirler provided between the tip of said air supply pipe and said coal-air supply pipe; and an intermediate whirler located at an inter-mediate point along the length of said coal-air supply pipe.

2. The burner according to claim 1 wherein said air whirler is secured to the tip of said protective pipe, said coal whirler is secured to the tip of said air supply pipe, and either one or both of said protective pipe and said air supply pipe is slidable in the axial direction.